1. Field of the Invention
The present invention relates to an active matrix liquid crystal display device, and more particularly relates to an in-plane switching mode active matrix liquid crystal display device.
2. Description of the Related Art
In recent years, an active matrix liquid crystal display (LCD) device using a thin film transistor (TFT) as a switching element of a pixel has been widely used. Operation modes of the LCD device described above include: a twisted nematic (TN) mode of rotating liquid crystal molecules in a direction perpendicular to a glass substrate; and a lateral electric field mode of rotating liquid crystal molecules in a direction parallel to a glass substrate. The lateral electric field mode is also called an in-plane switching (IPS) mode.
As shown in FIG. 8 or FIG. 9, in an IPS mode LCD device, normally, pixel electrodes 51 and common electrodes 52 are alternately formed so as to be parallel to each other on a TFT substrate 50. Accordingly, electric fields 53 between both electrodes change an orientation of liquid crystal molecules to control an amount of transmitted light. As described above, in the IPS mode, the liquid crystal molecules are rotated in a plane parallel to the substrate surface. Thus, the IPS mode has viewing angle characteristics better than those of the TN mode. As to such an IPS mode LCD device, for example, Japanese Patent Laid-open No. Hei 7-191336 has been known.
However, in the IPS mode LCD device of the related art, in order to reduce a drive voltage, the pixel electrodes 51 and the common electrodes 52 are arranged in a comb-teeth pattern and the comb-teeth-shaped electrodes are formed in an aperture. If the pixel electrodes 51 or the common electrodes 52 are formed of conductive films which are not transparent or have low light transmittance, aperture ratio is inevitably lowered.
Moreover, since the comb-teeth-shaped electrodes are formed on approximately the same plane, as shown in FIG. 9, a vertical electric field perpendicular to substrates 50 and 60 is also generated, besides a lateral electric field parallel to the substrates 50 or 60, between the comb-teeth-shaped electrodes. Accordingly, a uniform lateral electric field cannot be formed in a liquid crystal layer 70. Thus, the viewing angle characteristics may be deteriorated.
Moreover, since the comb-teeth-shaped electrodes are formed in an aperture, difference in level is formed by the comb-teeth-shaped electrodes in the aperture. Accordingly, in a rubbing treatment for controlling an initial alignment orientation of the liquid crystal molecules, rubbing dust is produced by the difference in level. Thus, inferior display characteristics such as a point defect may be caused by the rubbing dust.